While John R. Neill was easily the worst plotter of the six authors who contributed to what's come to be known as the Famous Forty, he did create some fascinating characters. Considering how often she appeared, his favorite might well have been Jenny Jump, a half-fairy girl from New Jersey. The Jenny Jump Mountain and State Forest are located in the northwestern part of the state, near Neill's own home in Flanders, and folk etymology says that they were named after a girl named Jenny who jumped in order to escape from one or more pursuing Minsi Indians. It's not entirely clear whether Neill intended this Jenny to be the same as his own character, but I believe his original Wonder City manuscript referred to her living in the mountains for a long time, and trying to charge rent to the fairies who lived there. In the published version, however, she's only fifteen when the story begins, and seemingly living alone (although I suppose it's possible her parents or guardians were just out at the time). She captures a leprechaun trying to steal her pepper-cheese, and he turns out to be her fairy godfather. I believe Neill originally called him Psychopompus, a variation on the term used for those who led the dead from this world to the next (the association of Odin with Hermes/Mercury was apparently because both gods served as psychopomps). While Jenny doesn't die, she does enter a new world after meeting the leprechaun, making his name appropriate. The book's editor, apparently fearing that a name like "Psychopompus" would be difficult to pronounce, changed it to "Siko Pompus," which brings to mind King Pompus of Pumperdink from Ruth Plumly Thompson's Oz books. But there's also a Neill drawing referring to the character as "Sico," so perhaps it went through several different spellings before the book was published.
Anyway, Jenny wishes for the leprechaun to turn her into a fairy, but due to a technicality, he stops after making her only HALF-fairy. Well, not exactly half. She gains heightened awareness in one eye and both ears, extra dexterity and other powers in eight of her fingers, and the power to launch herself into the air using one of her feet. She also breathes fire when she's angry, although it's never entirely clear whether this is due to a fairy mouth. She flies to Oz, where she befriends a Munchkin boy named Number Nine (his parents gave their children numbers for names), and takes advantage of his fondness for her in order to boss him around. Using a magical Turn-Style that she finds in a ruined house, she sets up a style shop in the Emerald City. She becomes rather popular, but her temper continues to cause trouble. In order to combat this, the Wizard of Oz makes her grow younger, losing her fairy powers (although I've heard that her reverse aging in the original manuscript was NOT the Wizard's doing, or at least not specifically attributed to him). When that fails, the Wizard physically removes her anger, envy, and ambition. That's what happens in the published book, anyway. I believe this lobotomy was not included in Neill's original manuscript, in which she learns how to better control her more negative traits on her own, but it is somewhat in character for the Wizard. After all, he replaced the Glass Cat's pink brains with transparent ones in order to make her more humble. She has the pink ones back in Magic, however, suggesting that messing with her mind might have been a failed experiment. And I like to think that much the same was the case with Jenny, who doesn't seem entirely free of anger and ambition in later books. Regardless, Ozma makes Jenny a Duchess, and Siko restores her fairy powers in the form of various odds and ends. And that's basically how she remains in Neill's other books.